Specifically when it's being used to ranch Fire Slimes. If you have a Charcoal Brick in there, Fire Slimes tend to be very happy and jump around a lot, leading to them jumping out of the ash trough. My idea is that there can be an upgrade to the Incinerator that's only purchasable when you have the Ash Trough upgrade: High Walls. It's very simple, but could help a lot!